This invention relates to a mixing apparatus for mixing cement, and particularly a gypsum cement composition, with water to form a slurry that is useful in forming floor underlayments and the like.
In the manufacturer of poured floors, cementitious aqueous slurries are produced and may be pumped to the site where flooring is to be poured. In the case of Portland cement slurries, the slurry ingredients (commonly cement, sand, aggregate and water) are charged to a vehicle-mounted mixer, and are mixed during the journey to the site where the cement is to be poured. With respect to poured gypsum floors, on the other hand, an appropriate mixing machine is provided at the building site, and sequential batches of a gypsum cement slurry are produced and are pumped through flexible tubing to the location, as in an apartment or office buildingxe2x80x94where flooring is to be poured. Cement mixing machines of this type are described in Jorgenson, U.S. Pat. Nos 4,075,374 and 4,159,912, the teachings of which are incorporated herein by reference.
Gypsum cement slurries consist of dry cement components (a gypsum cement formulation and sand) and water, and mixing is performed batch-wise, with each batch of fully mixed cement slurry being discharged into a holding container and from there being pumped to the pour location. Bags of gypsum cement composition commonly are trucked to the mixer location, and sand is often available nearby. Water can be obtained from a hydrant source if a hydrant is nearby, but often water is available only from nearby buildings and then only in amounts that can be transferred by a small hose such as a garden hose.
A typical batch of gypsum cement slurry may contain on the order of 30 gallons of water, and each batch is consumed in as little as 1 xc2xd minutes. Under these circumstances, water at the rate of 30 gallons per 1 xc2xd minutes (that is, at an average flow rate of 20 gallons per minute) is required, and small diameter (xc2xe to 1 inch diameter) garden hoses can provide water at this flow rate and commonly at pressures in the range of about 45 to about 80 psi gage pressure. However, in order to provide an appropriate mixing cycle, the dry cement ingredients and water must be charged to the mixing vessel so that mixing can occur for one minute or more to ensure production of a uniform slurry. In turn, the water component must be added to the mixing vessel in a time interval of about 15 seconds. If 30 gallons of water per batch are used, this requires an average flow rate of 120 gallons per minute to the mixing vessel, and garden hose sources of water simply are not capable of providing water at this flow rate.
One attempt to solve this problem involves providing a water tank substantially above the level of the mixer, and continuously discharging water from a garden hose-type source into the water tank. Water can be drawn from the water tank at a much more rapid rate, then, at the beginning of each mixing cycle. A two-fold problem arises. First, the amount of water discharged from the tank into a mixing vessel often is crudely measured by counting the number of seconds that a water valve is permitted to stay open, and it will be understood that substantial variation may occur in the amount of water charged to the mixing vessel. This, in turn, effects how well the slurry can be pumped, the ability of the slurry to self-level when poured upon a prepared surface, and the quality of the resulting floor underlayment. Second, the amount of water added from the garden hose source to the water tank is simply uncontrolled. If the tank is overfilled, water may escape from the water tank to mix with gypsum powder that may have spilled from bags, and gives rise to a messy workplace.
The problem outlined above has existed for 20 or more years, and no good solution appears to have been proposed. It would be desirable to provide a water supply for a mixer in which water could be accumulated in a controlled manner within a tank, and then could be discharged quickly into a mixer following which the process could be repeated. It would also be desirable to control with some accuracy the amount of water so discharged for the purpose of providing uniformity to sequential batches of the gypsum cement slurry.
I have found the above problems can be largely resolved through the use of a pressure tank having an internal diaphragm to receive water under pressure from a water source such as a garden hose, and to periodically and as needed discharge accurate volumes of water at a high flow rate into the mixing vessel.
In one embodiment, accordingly, my intention provides a mixing machine for mixing cement components with water to provide a pumpable slurry, the machine comprising a mixing vessel having an inlet for water and for dry cement components and a water tank for supplying water at a high flow rate to the mixing vessel. The water tank has an internal diaphragm separating the tank into water and air compartments, an inlet for admitting water to the water tank, a water outlet, and a conduit communicating the water tank with the mixing vessel and capable of accommodating the flow of water at an average flow rate substantially greater than the flow rate of water into the water compartment. The conduit includes a water meter and valve to monitor and regulate, respectively, the quantity of water supplied to the mixing vessel.
In another embodiment, the invention relates to a method of mixing cementitious materials with water to make a pumpable slurry. The method involves providing a mixing vessel having an inlet for water and for dry cement components, and a water tank for supplying water at a high flow rate to the mixing vessel and having an internal diaphragm separating the tank into water and air compartments. The water compartment of the tank is substantially filled with water from the source of water under pressure at a first average flow rate flow rate. A predetermined quantity of the water is discharged from the water compartment to the mixing vessel at a second flow rate substantially greater than the first average flow rate. The water is mixed in the mixing vessel with dry cement components to provide the slurry, and the slurry is discharged from the mixing vessel. The above steps are then repeated to permit batch after batch of the slurry to be rapidly formulated and mixed.